The invention relates to a method for producing a formed and at least regionally hardened sheet metal component. In particular, a sheet steel component with at least one perforation produced in it and method by which a blank is heated to forming temperature, subsequently formed in a tool and then at least regionally hardened by corresponding quenching The at least one perforation is produced in the blank in the course of a punching process before the blank is hardened. The invention further relates to a press hardening tool for producing a formed and at least partially hardened sheet metal component with at least two tool parts that can be adjusted relative to one another for the opening and closing of the tool as well as with a punch device comprising a punching stamp for producing a perforation in a blank located between the tool parts.
Press hardening tools are used to shape and harden metal blanks. Depending on the design of the hardening method, a blank that has been preheated correspondingly to forming temperature is fed to the press hardening tool, formed therein and after the forming has taken place is cooled sufficiently rapidly for it to harden and thus be tempered. Such press hardening tools are used, for example, for the manufacture of structural components of motor vehicles. The blanks are typically sheet steel parts so that the structural components are sheet steel components. It is also possible to further form already preformed sheet steel plates in a press hardening tool and to subsequently temper them within the tool. In principle, the heating of the blank to its forming temperature, typically corresponding to the austenitization temperature if the blank is made of steel, can be carried out within the press tool. However, the blank is usually heated in an oven to the forming temperature and then introduced into the opened press hardening tool. The press hardening tool itself has at least two tool parts that can be adjusted by opening and closing. As a rule these are referred to as the die and punch. The die here represents the tool part at rest, relative to which the punch is used by means of a press for closing the tool and thus for forming the blank inserted therein. To temper the shaped blank within the press hardening tool, the two tool parts have coolant channels through which a coolant is pumped. After the termination of the quenching process to at least regional harden the shaped blank, the tool is opened and the metal sheet component is removed.
Application cases exist in which such sheet components that are produced by the above-described method using a press hardening tool are to have one or more perforations, sometimes also called passages. Such perforations can be produced in the sheet steel component after the step of press hardening. This occurs by laser machining, since, due to the hardness established by the manufacturing process, a punching of the hardened sheet component is problematic. However, laser machining for producing the at least one perforation can also be disadvantageous. This is because of the costs incurred for equipment and handling. In addition, due to the heat input during the laser treatment, the hardness originally achieved is decreased at least in the marginal areas encompassing the perforation.
From DE 10 2004 019 693 A1 a method and a device for manufacturing a hardened sheet steel component are known, in which, within the press tool, the at least one perforation is produced in the blank during the quenching by perforating the blank. In this method, the at least one perforation is produced in the blank at a time when the latter has not yet hardened or in any case not yet completely hardened. The hole perforating stamp is removed from the perforation immediately after producing the perforation, in order to prevent the blank from shrinking onto the punching stamp. Because of this, damage to the punching stamp which occurs if said punching stamp is pulled off or out of a blank that has shrunk onto it during the course of the quenching process should be avoided.
However, in reference to the method known from DE 10 2004 019 693 A1, it is considered disadvantageous that the peripheral geometry of the at least one perforation produced in the blank is not controlled during the quenching process. It is true that the blank is held between the closed tool parts during the quenching process. However, this does not prevent shrinkage, particularly an irregular shrinkage of the opening width of the perforation produced. In principle, shrinkage of the opening width of the perforation has to be tolerated. However, it would be desirable for such shrinkage to occur uniformly over the perimeter of the perforation. This is not ensured with the above-mentioned previously known method. Different shrinkage rates can occur, particularly in the case of perforations whose geometry deviates from the circular cross sectional shape.
An additional method for manufacturing a hardened sheet metal profile with a perforation is known from EP 2 062 664 A1. In the method described in this document, a region delimited by at least one cut edge is first cut, wherein the cut depth is smaller than the material thickness of the plate. Subsequently, the plate is heat formed and the cut area is pushed out after the heat forming along the cut edge. The cutting and the pushing out of the area are carried out in opposite directions, so that burr-free cut contours are obtained. In this method as well as the already described method for DE 10 2004 019 693 A1, shrinkage events cannot prevented.